I live just a mile or two from the Montour Trail.
The Montour is not exactly the GAP but pretty darn close. We have a number of bridges and at least 3 tunnels which includes the National Tunnel.
Two problems with the Montour. It is nearly twice the distance to the start of the GAP from the airport area and the lower section is full of detours. Having a local guide helps a lot with detours.
Your other option is to go through the city. It is only 30 miles from my house to the start of the GAP. It is about 63 miles by way of the Montour.
There is a newly open trail that leads at least part way to the GAP and it is wonderful. All asphalt. It starts in Homestead (about 1/3 of the way from the city to the GAP). It gets you around the worst section of Route 837 (though I never thought 837 was that bad). Plus I have a fairly low stress route that gets you up to Homestead (the trail will go all the way from the city to the GAP in November, there is just a short but complicated section to complete).
Both routes are excellent options. It really depends on how much time you have and how much you are willing to put up with finding your way.
PM me. Assuming I am home, I would be happy to lead you either down the Montour or through the city. If you are flying in, I could pick you up at the airport, I live very close. Friday night or Saturday arrival is always best for me.
Last edited by spinnaker; 06-08-11 at 10:12 AM.